Centrifugal technique can be applied to the model tests of bearing capacity, earth pressure, anchor pullout, etc. in sand. In this method, the soil mechanics law of similarity is satisfied by performing the model tests in the centrifugal field. However, the problems on the grain size of soil and the magnitude of acceleration of the test field have not been clarified. In this paper, the scale effect will be discussed based on the model tests of the anchor pullout resistance in dry sand by the centrifugal technique and the conventional model test in 1 g field. Important findings are : (1) no scale effect can be observed in the centrifugal model test for the O.1∼1.O mm grain size of sand and for the approximately 10 mm width or diameter of model anchor, and (2) since the scale effect is observed even by the centrifugal technique, the acceleration level must be set considering the scale effect.

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In two recent papers the authors have shown that : a) the behaviour of clays during one-dimensional compression is controlled in laboratory by a unique stress-strain-strain rate relationship; b) the oedometer curve obtained in laboratory at the end of primary consolidation underestimates in situ settlements. In this paper, the applicability of the stress-strain-strain rate model established in laboratory is examined in in situ conditions under three different test embankments. It is shown that the model applies well to in situ conditions at large strains ; on the contrary, at small strains, probably because of disturbance and stress paths, at a given strain and strain rate, the in situ effective stress is higher than the laboratory one.

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The recent developments of human activities in marine environments are stimulating engineering concerns on natural hazards in the sea. One of the hazards in the marine environments is a failure of submarine slopes which is caused by earthquakes, wave action, rapid sedimentation, etc. The submarine soil flow as a consequence of slope instability is possible to be of gigantic scale, and affects artificial facilities in vast area, requiring them to be well protected against soil's attack. A series of model tests were carried out to understand the intensity of the drag force which is brought about by a mudflow on a cylindrical solid column. The test results indicate that the intensity of the drag force is proportional to the embedment and diameter of the column, while practically independent of the flow velocity. Since the water content of flowing soil was found to be playing an important role, its effects were accounted for through undrained shear strength of soil. The shear strength of very soft slurry employed here was evaluated either by a model-footing test or by an empirical equation, both of which gave identical results. Eventually an empirical equation is proposed to predict the magnitude of the drag force exerted by a flow of clay slurry.

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Piecewise linear approximation technique is newly applied for describing multi-dimensional elasto-plastic consolidation deformation behaviour of a normally consolidated clay foundation. The stiffness factor of clay foundation in terms of effective stresses can be determined from time to time by applying the linearization technique to observations of non-linear consolidation deformation behaviour of the foundation. When gradual load application such as an execution stage of embanking with finite width is considered, although shear deformation of the clay should proceed under partially drained condition, the stiffness factor of the clay foundation is still found to deteriorate. On the other hand, when consolidation becomes more predominant than shear deformation, the stiffness factor will recover its value from the deteriorated state. This is typically found just after the finish of embanking, although consolidation never proceeds without the occurrence of a considerable amount of shear deformation even in the halt of external loading. Thus, it is found that the partially drained behaviour of clay deformation in which consolidation proceeds with shear deformation is well described by monitoring the process of deterioration and recovery of the stiffness factor of a clay foundation. The piecewise linear approximation technique gives this monitoring procedure. The developed procedure is applied to the observational method of predicting consolidation settlement.

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The method of slope stability analysis during rainfall employed in the present study is based on the combination of simplified unsaturated seepage analysis and usual circular arc stability analysis, and the method can evaluate not only both the reduction of soil strength along slip surface and the increase of self weight of slope due to seepage but also some other factors such as rainfall intensity, antecedent precipitation, vegetation, slope protection, weathering and spring water. The effects of these factors on the stability of the slope are evaluated in terms of the reduction of soil strength through introducing new parameter of strength reduction. The linear regression analysis will be made for evaluating the new strength reduction parameter using field observations and the data of the past case records of slope failures due to rainfall. By applying the Bayesian method to the linear regression analysis the probabilistic slope failure prediction is also shown to be available. The numerical simulations for the developed procedure has made the each effect of those factors on the stability of slopes clear and distinct. The developed procedure is applied for a case record of slope failure using actual rainfall observations. The risk of slope failure calculated by the developed method increases rapidly just before the observation of actual slope failure. The effect of the slope protection by the use of concrete spraying on the stabilization of slope is also shown to be well evaluated by the developed procedure.

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Salient features of the mechanics of consolidation are studied in the light of a consistent fundamental approach. In particular, it is pointed out that in an Eulerian formulation, the material derivative contains a convective term involving the solid phase velocity. The significance of convectionis then studied by solving a one-dimensional problem twice, once with convection and once neglecting it. As expected, when the strain is small, the convective effect is negligible and for large strain, it becomes very significant. A scheme, conceptually similar to the updated lagrangian scheme, is then introduced. The procedure is illustrated and the correctness of the concept verified by incorporating the concept in a finite difference calculation to solve a one-dimensional problem. This approach is applicable to multi-dimensional problems, for which the Eulerian governing equations are normally used.

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Vertical drains are usually installed in alluvial weak subsoil consisting of several layers. Several existing solutions of centripetal consolidation considering the well resistance are available. Those are, however, inapplicable for multilayered ground. Taking well resistance into account, a numerical analysis method is presented in this study to solve the consolidation problem in multilayered anisotropic clayey subsoil in which vertical drains have been installed. The analytic results coincide well with the observed results obtained through a pair of in-situ consolidation tests. As a consequence of calculations for many cases of two-layered problems where both degree of heterogeneity and thickness ratio between the 1st and the 2nd layer differ from each other, it is indicated that the consolidation of a two-layered ground is significantly retarded than that of the single-layered ground whose coefficient of consolidation is equal to the mean value of the two-layered ground. A new procedure is next proposed for predicting the consolidation degree of multilayered ground using existing equations concerning single-layered centripetal consolidation. The accuracy of this procedure is discussed in comparison with the numerical results. The experimental results also reveal that the proposed procedure yields a sufficiently accurate consolidation curve for multilayered ground without the need for a computer.

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Various base bearing capacity formulae for piles have been proposed based on the rigid-plastic theory and/or the elasto-plastic cavity expansion theory. None of them, however, can explain the multiphase phenomena of failure patterns : i.e., (1) general, (2) local, and (3) punching shear failure modes. Firstly, three base bearing capacity formulae corresponding to the abovementioned failure modes in cohesionless soils were discussed. It was then interpreted that the ultimate base resistance of a pile may be estimated from the minimum in the values calculated by those formulae, i.e. Min. ((1), (2). (3)). Large model pile tests in sands, whose data have been published, were analyzed using the unified formula proposed. The results can explain the phenomena having been pointed out from experiments; e.g., a pile whose embedded depth is larger than a certain depth never fails in general shear failure mode and the certain depth depends on the sand density. The formula proposed indicates that the dilatancy property has great influence on the mechanism and magnitude of the base resistance. As the application of the formula proposed, the scale effect in the transposition of the results of in-situ penetration tests on the ultimate base bearing capacity of piles was discussed and 4 pile-diameters above the pile base and 6 pile-diameters below the pile base have been suggested as the influence zone.

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When a saturated clay is subjected to the seismic cyclic shear, excess pore water pressure is produced. After the dissipation of the accumulated excess pore pressure, the void ratio may become so small that the clay layer settles considerably. The characteristics of the settlement under these conditions should be clarified to estimate the long term behavior of the structures constructed on the soft clayey ground. In this paper, two-way strain controlled cyclic simple shear tests under the undrained condition are carried out for normally consolidated and overconsolidated Kaolinite clay. Subsequently, the excess pore water pressure are dissipated and then the settlement are measured. From the results, it is clarified that 1) the excess pore water pressure produced during cyclic shear depends on the amplitude of cyclic shear strain, number of cycles and the overconsolidation ratio, 2) the seismic settlement of the clayey ground depends on the excess pore water pressure accumulated during cyclic shear, and the overconsolidation ratio, 3) the seismic settlement is considerably large compared with the settlement produced by the secondary compression.

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This paper offers the estimation formulas of the pullout resistance of plate anchor in medium-to-dense sandy soil. The soil failure mechanism of anchor pullout can be divided into shallow and deep mechanisms. The solution of shallow anchor by Meyerhof (1973) and the formula of deep horizontal anchor by the theory of plasticity with the concept of cavity expansion will be introduced, and compared with the results of centrifuge model tests and the results of elastoplastic finite element analyses. The main conclusions are as follows : (1) The solutions of the shallow anchor in arbitrary inclination and the deep horizontal anchor, the results of centrifuge model tests, and the results of finite element analyses showed good agreement; (2) The shape factor of finite length anchor has been clarified experimentally; (3) The critical relative depth from shallow anchor to deep anchor is 6-8 in the case of medium-to-dense dry sand having the angle of shear resistance of 32°-42°.

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This paper describes the strength and deformation properties of a clean sand (Toyoura sand) in torsional simple shear under the drained condition. It was found that the dependency on pressure level of both the angle of internal friction φ=arcsin {(σ₁'-σ₃')/(σ₁'+σ₃')}_max and the relationship between the stress ratio σ₁'/σ₃', the shear strain γ_max=ε₁-ε₃ and the volumetric strain ε_υ=ε₁+ε₃ at relatively large strains is very small when σ₃' is less than about O.5 kgf/cm² (49 kN/m²). These results are well in accordance with those previously obtained for the sand by the triaxial compression tests, the plane strain compression tests and the torsional shear tests on isotropically consolidated specimens. The results of the present tests show that the relationships between σ₁'/σ₃', γ_max and ε_υ and the stress states in terms of b=(σ₂'-σ₃')/(σ₁'-σ₃') at relatively large strains in simple shear are very similar to those by the plane strain compression test in which the directions of principal stresses with respect to the fabric of the specimen are fixed to the values in the simple shear tests at relatively large strains. The angle of friction φ^* in simple shear defined in the conventional way as arctan (τ_at/σ_a')_max (τ_at/σ_a' is the stress ratio on the horizontal plane of shearing) was found less than φ by about 14%. It was found that φ in simple shear is well comparable with that in plane strain compression only when the directions of principal stresses with respect to the fabric of specimen are the same in the both testing methods.

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This paper presents some types of the damage caused by the Michoacan, Mexico Earthquake of September 19, 1985 and describes the relations between those damage and their ground conditions based on the site investigation in Mexico City and the epicentral zone in January, 1986. The lessons learned from the Mexico Earthquake through the site investigation, are summarized as follows. (1) Tremendous damage in Mexico City at 400 km distance from the epicenter, was triggered by the amplifications of the ground motions through the soft lacustrine clay deposit which is surrounded by hard volcanic rock formations. (2) At the epicentral zone the damage to structures was relatively small in consideration of the recorded values of the peak acceleration which are 150 to 170 gals because most of structures stand on the firm coastal terrace. Only the City of Lazaro Cardenas, which was developed on the alluvial low ground, were severely attacked by the earthquake. Especially the factories on the reclaimed land were damaged due to the liquefactions. (3) Comparison between the microtremor measurement on La Villita Dam and the FEM analysis suggests that the dam responded to the earthquake as a high dam adding the thickness of the foundation to the height of the dam. (4) In the City of Guzman which is located 200km to the northwest of the epicenter and developed in the basin like Mexico City, most of the houses and pavements were damaged along the small gaps which were considered to relate a fault existing under the ground in the volcanic topography.

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The finite difference method is applied to numerical analysis of the effectiveness of gravel drains constructed to prevent liquefaction of sandy soils due to earthquake motion. The basic equation used here is the axisymmetric diffusion equation which includes the generation of excess pore water pressure. The arcsin function of the equivalent cycle ratio formulated by Seed and Booker is used as the pore pressure buildup curve under undrained conditions. A comparison with the results of in-situ experiments reveals that the well resistance of the drain wells should be considered in the gravel drain design, and that the numerical method is valid for the pore pressure prediction. The analytical results are summarized as a set of diagrams in order to provide a convenient basis for the drain spacing design which takes well resistance into account. These diagrams permit drain spacing to be directly decided without the need for a computer. The application range of these diagrams is markedly wider than those of several existing diagrams currently used.

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Some of the observations published so far represent that secondary compression arises not only after the dissipation of pore water pressure but also during the stage of primary consolidation. The secondary compression has considerable influence upon the time-strain relation in the process of consolidation and makes the estimate of consolidation difficult, in the case that primary consolidation continues for a long time. Therefore, it is of significance to investigate the secondary compression and its characteristics for the sake of evaluating more reasonably the consolidation of a clay deposit. This technical note is mainly concerned with the characteristics of secondary compression in the stage that pore water pressure is dissipated. From the results of consolidation tests which have been carried out on a clay with three kinds of thickness, the following findings have been derived. (1) The amount of a strain due to secondary compression developed in the stage of primary consolidation enlarges as the thickness of a clay layer increases. (2) Secondary compression occurs during primary consolidation only when the effective pressure is greater than the quasi-preconsolidation pressure and may be expressed as a function of elapsed time and a compression strain. On the other hand, no secondary compression may arise during primary consolidation when a clay stays in an apparently over-consolidated state.

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